[effects/sheet] Modernize code

Summary:
* Use new connect syntax
* Fix coding style
* Port to TimeLine
* Delete unused includes
* Use interpolate helper
* Drop WindowInfo class

Behavior of this effect hasn't been changed.

Test Plan: Opened/closed an "Open File" dialog, it still flies in/out.

Reviewers: #kwin, davidedmundson

Reviewed By: #kwin, davidedmundson

Subscribers: davidedmundson, anthonyfieroni, kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D14685